Ultralow dielectric constant material as an intralevel or interlevel dielectric in a semiconductor device and electronic device made

ABSTRACT

A method for fabricating a thermally stable ultralow dielectric constant film comprising Si, C, O and H atoms in a parallel plate chemical vapor deposition process utilizing plasma enhanced chemical vapor deposition (“PECVD”) process is disclosed. Electronic devices containing insulating layers of thermally stable ultralow dielectric constant materials that are prepared by the method are further disclosed. To enable the fabrication of thermally stable ultralow dielectric constant film, specific precursor materials are used, such as, cyclic siloxanes and organic molecules containing ring structures, for instance, tetramethylcycloterasiloxane and cyclopentene oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part application ofU.S. Ser. No. 10/176,438, filed Jun. 19, 2002, which is a divisionalapplication of U.S. Ser. No. 09/769,089, filed Jan. 25, 2001, now U.S.Pat. No. 6,441,491 and the present application also claims benefit ofU.S. Provisional Application Serial No. 60/243,169, filed Oct. 25, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field of the Invention

[0003] The present invention generally relates to a method forfabricating a dielectric material that has an ultralow dielectricconstant (or ultralow-k) associated therewith and an electronic devicecontaining such a dielectric material. More particularly, the presentinvention relates to a method for fabricating a thermally stableultralow-k film for use as an intralevel or interlevel dielectric in anultra-large-scale integration (“ULSI”) back-end-of-the-line (“BEOL”)wiring structure and an electronic structure formed by such method.

[0004] 2. Description of the Prior Art

[0005] The continuous shrinking in dimensions of electronic devicesutilized in ULSI circuits in recent years has resulted in increasing theresistance of the BEOL metallization as well as increasing thecapacitance of the intralayer and interlayer dielectric. This combinedeffect increases signal delays in ULSI electronic devices. In order toimprove the switching performance of future ULSI circuits, lowdielectric constant (k) insulators and particularly those with ksignificantly lower than silicon oxide are needed to reduce thecapacitances. Dielectric materials (i.e., dielectrics) that have low-kvalues have been commercially available. For instance, one of suchmaterials is polytetrafluoroethylene (“PTFE”), which has a k value of2.0. However, these dielectric materials are not thermally stable whenexposed to temperatures above 300˜350° C. Integration of thesedielectrics in ULSI chips requires a thermal stability of at least 400°C. Consequently, these dielectrics are rendered useless duringintegration.

[0006] The low-k materials that have been considered for applications inULSI devices include polymers containing Si, C, O, such asmethylsiloxane, methylsilsesquioxanes, and other organic and inorganicpolymers. For instance, a paper (N. Hacker et al. “Properties of new lowdielectric constant spin-on silicon oxide based dielectrics.” Mat. Res.Soc. Symp. Proc. 476 (1997): 25) described materials that appear tosatisfy the thermal stability requirement, even though some of thesematerials propagate cracks easily when reaching thicknesses needed forintegration in the interconnect structure when films are prepared by aspin-on technique. Furthermore, the precursor materials are high costand prohibitive for use in mass production. In contrast to this, most ofthe fabrication steps of very-large-scale-integration (“VLSI”) and ULSIchips are carried out by plasma enhanced chemical or physical vapordeposition techniques. The ability to fabricate a low-k material by aplasma enhanced chemical vapor deposition (“PECVD”) technique usingreadily available processing equipment will simplify the material'sintegration in the manufacturing process, reduce manufacturing cost, andcreate less hazardous waste. U.S. Pat. Nos. 6,147,009 and 6,497,963assigned to the common assignee of the present invention andincorporated herein by reference in their entirety, described anultralow dielectric constant material, consisting of Si, C, O and Hatoms, having a dielectric constant not more than 3.6, and exhibitingvery low crack propagation velocities.

[0007] U.S. Pat. Nos. 6,312,793, 6,479,100 and 6,312,797 assigned to thecommon assignee of the present invention and incorporated herein byreference in their entirety, described a dual-phase material, consistingof a matrix composed of Si, C, O, and H atoms, a phase composed ofmainly C and H atoms, and having a dielectric constant of not more than3.2. It should be noted that continued reduction of the dielectricconstant of such materials will further improve the performance ofelectronic devices incorporating such dielectrics.

[0008] In view of the foregoing, there is a continued need fordeveloping a dielectric material that has a dielectric constant of notmore than about 2.8 and inhibits cracking.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the present invention to provide amethod for fabricating an ultralow dielectric constant material having adielectric constant of not more than about 2.8. More preferably, thedielectric constant for the ultralow-k material is in a range of about1.5 to about 2.5, and most preferably, the dielectric constant is in arange of about 2.0 to about 2.25. It should be noted that all dielectricconstants are relative to a vacuum unless otherwise specified.

[0010] It is another object of the present invention to provide a methodfor fabricating an ultralow dielectric constant material comprising Si,C, O and H atoms from a mixture of at least two precursors, wherein oneprecursor is selected from molecules with ring structures comprisingSiCOH components and the second precursor is an organic moleculeselected from the group consisting of molecules with ring structures.

[0011] It is a further object of the present invention to provide amethod for fabricating an ultralow dielectric constant film in aparallel plate plasma enhanced chemical vapor deposition (“PECVD”)reactor.

[0012] It is yet a further object of the present invention to provide animproved method for fabricating an ultralow dielectric constant materialby depositing a film on a substrate in the presence of inert gas, suchas He or Ar, thereby improving uniformity of the film deposited andstabilizing the plasma within the PECVD reactor.

[0013] It is another object of the present invention to provide a methodfor fabricating an ultralow dielectric constant material for use inelectronic structures as an intralevel or interlevel dielectric in aback-end-of-the-line (“BEOL”) interconnect structure.

[0014] It is yet another object of the present invention to provide athermally stable ultralow dielectric constant material that has lowinternal stresses and a dielectric constant of not higher than about2.8. More preferably, the dielectric constant for the ultralow-kmaterial is in a range of about 1.5 to about 2.5 and, most preferably,the dielectric constant is in a range of about 2.0 to about 2.25.

[0015] It is still another object of the present invention to provide anelectronic structure incorporating layers of insulating materials asintralevel or interlevel dielectrics in a back-end-of-the-line (“BEOL”)wiring structure in which at least two of the layers of insulatingmaterials comprise an ultralow dielectric constant material of thepresent invention.

[0016] It is yet a further object of the present invention to provide anelectronic structure, which has layers of the inventive ultralowdielectric constant material as intralevel or interlevel dielectrics ina back-end-of-the-line (“BEOL”) wiring structure and which furthercontains at least one dielectric cap layer as a reactive ion etch(“RIE”) mask polish stop or a diffusion barrier.

[0017] In accordance with the present invention, there is provided amethod for fabricating a thermally stable dielectric material that has amatrix comprising Si, C, O, and H atoms and an atomic levelnanoporosity. In a preferred embodiment, the dielectric material has amatrix that consists essentially of Si, C, O, and H. The presentinvention further provides a method for fabricating the dielectricmaterial by reacting a first precursor gas comprising atoms of Si, C, O,and H and at least a second precursor gas comprising atoms of C, H, andoptionally O, F and N in a plasma enhanced chemical vapor deposition(“PECVD”) reactor. The present invention further provides an electronicstructure (i.e., substrate) that has layers of insulating materials asintralevel or interlevel dielectrics used in a back-end-of-the-line(“BEOL”) wiring structure, wherein the insulating material can be theultralow-k film of present invention.

[0018] In a preferred embodiment, there is provided a method forfabricating a thermally stable ultralow dielectric constant (ultralow-k)film comprising the steps of: providing a plasma enhanced chemical vapordeposition (“PECVD”) reactor; positioning an electronic structure (i.e.,substrate) in the reactor; flowing a first precursor gas comprisingatoms of Si, C, O, and H into the reactor; flowing a second precursorgas mixture comprising atoms of C, H and optionally O, F and N into thereactor; and depositing an ultralow-k film on the substrate. Preferably,the first precursor is selected from molecules with ring structurescomprising SiCOH components such as1,3,5,7-tetramethylcyclotetrasiloxane (“TMCTS” or “C₄H₁₆O₄Si₄”). Thesecond precursor may be an organic molecule selected from the groupconsisting of molecules with ring structures, preferably with more thanone ring present in the molecule. Especially useful, are speciescontaining fused rings, at least one of which contains a heteroatom,preferentially oxygen. Of these species, the most suitable are thosethat include a ring of a size that imparts significant ring strain,namely rings of 3 or 4 atoms and/or 7 or more atoms. Particularlyattractive, are members of a class of compounds known as oxabicyclics,such as cyclopentene oxide (“CPO” or “C₅H₈O”).

[0019] Optionally, the deposited film of the present invention can beheat treated at a temperature of not less than about 300° C. for a timeperiod of at least about 0.25 hour. The method may further comprise thestep of providing a parallel plate reactor, which has an area of asubstrate chuck between about 300 cm² and about 800 cm², and a gapbetween the substrate and a top electrode between about 1 cm and about10 cm. A high frequency RF power is applied to one of the electrodes ata frequency between about 12 MHZ and about 15 MHZ. Optionally, anadditional RF power can be applied to the same or different electrode.The heat-treating step may further be conducted at a temperature nothigher than about 300° C. for a first time period and then at atemperature not lower than about 380° C. for a second time period, thesecond time period being longer than the first time period. The secondtime period may be at least about 10 times the first time period.

[0020] The deposition step for the ultralow dielectric constant film ofthe present invention may further comprise the steps of: setting thesubstrate temperature at between about 25° C. and about 400° C.; settingthe high frequency RF power density at between about 0.05 W/cm² andabout 4.0 W/cm², preferably from greater than 0.5 W/cm² to about 4.0W/cm², and even more preferably from greater than 2.0 W/cm² to about 4.0W/cm²; setting the first precursor flow rate at between about 5 sccm andabout 1000 sccm; setting the flow rate of the second precursor betweenabout 5 sccm and about 50,000 sccm, preferably from greater than 1000sccm to about 50,000 sccm; setting the reactor pressure at a pressurebetween about 50 mTorr and about 5000 mTorr; and setting the highfrequency power between about 15 W and about 500 W. Optionally, anotherRF power may be added to the plasma between about 10 W and about 300 W.When the area of the substrate chuck is changed by a factor of X, the RFpower applied to the substrate chuck is also changed by a factor of X.

[0021] In another preferred embodiment, there is provided a method forfabricating an ultralow-k film comprising the steps of: providing aparallel plate type chemical vapor deposition reactor that has plasmaenhancement; positioning a pre-processed wafer on a substrate chuckwhich has an area of between about 300 cm² and about 800 cm² andmaintaining a gap between the wafer and a top electrode between about 1cm and about 10 cm; flowing a first precursor gas comprising cyclicsiloxane molecules into the reactor; flowing at least a second precursorgas comprising organic molecules with ring structures including C, H andO atoms; and depositing an ultralow-k film on the wafer. The process mayfurther comprise the step of heat-treating the film after the depositionstep at a temperature of not less than about 300° C. for at least about0.25 hour. The process may further comprise the step of applying a RFpower to the wafer. The heat-treating step may further be conducted at atemperature of not higher than about 300° C. for a first time period andthen at a temperature not lower than about 380° C. for a second timeperiod, the second time period being longer than the first time period.The second time period may be at least about 10 times the first timeperiod.

[0022] The cyclic siloxane precursor utilized can betetramethylcyclotetrasiloxane (“TMCTS”) and the organic precursor can becyclopentene oxide (“CPO”). The deposition step for the ultralow-k filmmay further comprise the steps of: setting the wafer temperature atbetween about 25° C. and about 400° C.; setting a RF power density atbetween about 0.05 W/cm² and about 4.0 W/cm², preferably greater than2.0 W/cm² to about 4.0 W/cm²; setting the flow rate of the cyclicsiloxane between about 5 sccm and about 1000 sccm; setting the flow rateof the organic precursor between about 5 sccm and about 50,000 sccm,preferably greater than 1000 sccm to about 50,000 sccm; and setting thepressure in the reactor at between about 50 mTorr and about 5000 mTorrand depositing a dielectric film on the wafer in the presence of aninert gas such as He, Ar, Ne, Kr or Xe. Additionally, the depositionstep may further comprise setting a flow ratio of cyclopentene oxide totetramethylcyclotetrasiloxane to between about 1 and about 80,preferably between 10 and 60. The area of the substrate chuck can bechanged by a factor X, which leads to a change in RF power by the samefactor X.

[0023] In still another preferred embodiment, there is provided a methodfor fabricating a thermally stable ultralow-k dielectric film comprisingthe steps of: providing a plasma enhanced chemical vapor depositionreactor of a parallel plate type; positioning a wafer on a substratechuck that has an area between about 300 cm² and about 800 cm² andmaintaining a gap between the wafer and a top electrode between about 1cm and about 10 cm; flowing a precursor gas mixture of a cyclic siloxanewith a cyclic organic molecule into the reactor over the wafer, which iskept at a temperature between about 60° C. and about 200° C., at a totalflow rate between about 25 sccm and about 5000 sccm, preferably greaterthan 500 sccm to about 5000 sccm, while keeping the reactor pressure atbetween about 100 mTorr and about 5000 mTorr; depositing a dielectricfilm on the wafer under a RF power density between about 0.25 W/cm² andabout 4 W/cm², preferably greater than 0.8 W/cm² to about 4 W/cm²; andannealing the ultralow-k film at a temperature of not less than about300° C. for at least about 0.25 hour. The inventive method may furthercomprise the step of annealing the film at a temperature of not higherthan about 300° C. for a first time period and then at a temperature notlower than about 380° C. for a second time period, wherein the secondtime period is longer than the first time period. The second time periodmay be set at least about 10 times the first time period. The cyclicsiloxane precursor can be tetramethylcyclotetrasiloxane (“TMCTS”) andthe cyclic organic precursor can be cyclopentene oxide (“CPO”).

[0024] The present invention is further directed to an electronicstructure which has layers of insulating materials as intralevel orinterlevel dielectrics in a back-end-of-the-line (“BEOL”) interconnectstructure which includes a pre-processed semiconducting substrate thathas a first region of metal embedded in a first layer of insulatingmaterial, a first region of conductor embedded in a second layer ofinsulating material of the inventive ultralow-k dielectric, theultralow-k dielectric comprising Si, C, O and H, and a multiplicity ofnanometer-sized pores, and having a dielectric constant of not more thanabout 2.8, the second layer of insulating material being in intimatecontact with the first layer of insulating material, the first region ofconductor being in electrical communication with the first region ofmetal, and a second region of conductor being in electricalcommunication with the first region of conductor and being embedded in athird layer of insulating material comprising the inventive ultralow-kdielectric, the third layer of insulating material being in intimatecontact with the second layer of insulating material. The electronicstructure may further comprise a dielectric cap layer situatedin-between the second layer of insulating material and the third layerof insulating material. The electronic structure may further comprise afirst dielectric cap layer between the second layer of insulatingmaterial and the third layer of insulating material, and a seconddielectric cap layer on top of the third layer of insulating material.

[0025] The dielectric cap material can be selected from silicon oxide,silicon nitride, silicon oxynitride, a refractory metal silicon nitride(wherein the refractory metal is selected from the group consisting ofTa, Zr, Hf and W), silicon carbide, carbon doped oxide or SiCOH andtheir hydrogenated compounds. The first and the second dielectric caplayers may be selected from the same group of dielectric materials. Thefirst layer of insulating material may be silicon oxide or siliconnitride or doped varieties of these materials, such as phosphorussilicate glass (“PSG”) or boron phosphorus silicate glass (“BPSG”). Theelectronic structure may further include a diffusion barrier layer of adielectric material deposited on at least one of the second and thirdlayers of insulating material. The electronic structure may furthercomprise a dielectric on top of the second layer of insulating material,which acts as a reactive ion etch (“RIE”) hard mask and polish stoplayer and a dielectric diffusion barrier layer on top of the dielectricRIE hard mask and polish stop layer. The electronic structure mayfurther comprise a first dielectric RIE hard mask/polish-stop layer ontop of the second layer of insulating material, a first dielectric RIEhard mask/diffusion barrier layer on top of the first dielectricpolish-stop layer, a second dielectric RIE hard mask/polish-stop layeron top of the third layer of insulating material, and a seconddielectric diffusion barrier layer on top of the second dielectricpolish-stop layer. The electronic structure may further comprise adielectric cap layer of same materials as mentioned above, between aninterlevel dielectric of ultralow-k dielectric and an intraleveldielectric of ultralow-k dielectric.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The foregoing objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

[0027]FIG. 1 depicts the general electronic structure of a bicyclicether, also known as a oxabicyclic, which is a preferred compound forthe second precursor. In this general schematic, the compound includestwo rings, one of which contains an oxygen atom. The size of each ringis determined by the number of repeating methylene groups in each cycle,m and n. In a highly preferred case of cyclopentene oxide, m=0 and n=2.

[0028]FIG. 2 depicts the general electronic structure of an unsaturatedbicyclic ether, also known as a unsaturated oxabicyclic, which is apreferred compound for the second precursor. In this general schematic,the compound includes two rings, one of which contains an oxygen atom.The size of each ring is determined by the number of repeating methylenegroups in each cycle, l, m and n. The position of the unsaturated bondis determined by m and n. In the example of 9-oxabicylo[6.1.0]non-4-ene,l=0, m=2 and n=2.

[0029]FIG. 3 depicts a cross-sectional view of a parallel plate chemicalvapor deposition reactor according to the present invention.

[0030]FIG. 4 depicts a Fourier Transform Infrared (“FTIR”) spectrumobtained from a SiCOH film deposited from a mixture oftetramethylcyclotetrasiloxane (“TMCTS”) and He.

[0031]FIG. 5 depicts a FTIR spectrum obtained from the inventiveultralow-k material deposited from a mixture of TMCTS+HE andcyclopentene oxide according to the present invention.

[0032]FIG. 6 depicts an enlarged, cross-sectional view of an electronicdevice having an intralevel dielectric layer and an interleveldielectric layer of ultralow-k material according to the presentinvention.

[0033]FIG. 7 depicts an enlarged, cross-sectional view of the electronicstructure of FIG. 6 having an additional diffusion barrier dielectriccap layer on top of the ultralow-k material film according to thepresent invention.

[0034]FIG. 8 depicts an enlarged, cross-sectional view of the electronicstructure of FIG. 7 having an additional RIE hard mask/polish-stopdielectric cap layer and dielectric cap diffusion barrier on top of thepolish-stop layer according to the present invention.

[0035]FIG. 9 depicts an enlarged, cross-sectional view of the electronicstructure of FIG. 8 having additional RIE hard mask/polish-stopdielectric layers on top of the interlevel ultralow-k material filmaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0036] The present invention discloses a method for fabricating athermally stable ultralow dielectric constant film in a parallel plateplasma enhanced chemical vapor deposition (“PECVD”) reactor. Thematerial disclosed in the preferred embodiment contains a matrix of ahydrogenated oxidized silicon carbon material (SiCOH) comprising Si, C,O and H in a covalently bonded network and having a dielectric constantof not more than about 2.8, which may further contain molecular scalevoids, approximately 0.5 to 20 nanometer in diameter, further reducingthe dielectric constant to values below about 2.0. More preferably, thedielectric constant for the ultralow-k film is in a range of about 1.5to about 2.5, and most preferably the dielectric constant is in a rangeof about 2.0 to about 2.25. To produce an ultralow-k thermally stablefilm, a specific geometry of the deposition reactor with specific growthconditions is necessary. For instance, in the parallel plate reactor, anarea of the substrate chuck should be between about 300 cm² and about800 cm², with a gap between the substrate and a top electrode betweenabout 1 cm and about 10 cm. A RF power is applied to one of theelectrodes. In accordance with the present invention, the ultralowdielectric constant film is formed from a mixture of a cyclic siloxaneprecursor such as TMCTS and a second precursor, which is an organicmolecule, selected from the group consisting of molecules with ringstructures, such as cyclopentene oxide, in the presence of an inert gas,in a specifically configured reaction reactor under specific reactionconditions. The low dielectric constant film of the present inventioncan further be heat treated at a temperature not less than about 300° C.for at least about 0.25 hour to reduce the dielectric constant. Duringthis heat treatment step, molecule fragments derived from the secondprecursor gas (or gas mixture) comprising carbon and hydrogen andoptionally oxygen atoms may thermally decompose and may be convertedinto smaller molecules which are released from the film. Optionally,further development of voids may occur in the film by the process ofconversion and release of the molecule fragments. The film density isthus decreased.

[0037] The present invention provides a method for preparing a materialthat has an ultralow dielectric constant, i.e., lower than about 2.8,which is suitable for integration in a BEOL wiring structure. Morepreferably, the dielectric constant for the inventive ultralow-k film isin a range of about 1.5 to about 2.5 and, most preferably, thedielectric constant is in a range of about 2.0 to about 2.25. Theinventive films can be prepared by choosing at least two suitableprecursors and a specific combination of processing parameters asdescribed herein below. Preferably, the first precursor is selected frommolecules with ring structures comprising SiCOH components such as1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS or C₄H₁₆O₄Si₄) oroctamethylcyclotetrasiloxane (OMCTS or C₈H₂₄O₄Si₄). More generally, thefirst precursor is of a class of cyclic alkylsiloxanes comprising a ringstructure including an equivalent number of Si and O atoms bonded in analternating fashion to which alkyl groups (such as methyl, ethyl, propylor higher or branched analogs as well as cyclic hydrocarbons such ascyclopropyl, cyclopentyl, cyclohexyl, and higher analogs) are covalentlybonded to at least one of the silicon atoms, including the cases whereall the silicon atoms have two alkyl groups attached. Such alkyl groupsmay be similar or dissimilar. Additionally, the silicon atoms of suchcyclic siloxanes may be bonded to hydrogen, in which case thesecompounds may be considered partially alkylated hydrosiloxanes.

[0038] The second precursor may be chosen from organic molecules,containing C, H, and O atoms and containing at least one ring, that havesuitable volatility such that they may be introduced to the depositionreactor as a vapor by manipulation of temperature and pressure.Additionally, other atoms such as N, S, Si, or halogens may be containedin the precursor molecule. Additionally, more than one ring may bepresent in the precursor molecule. Especially useful, are speciescontaining fused rings, at least one of which contains a heteroatom,preferentially oxygen. Of these species, the most suitable are thosethat include a ring of a size that imparts significant ring strain,namely rings of 3 or 4 atoms and/or 7 or more atoms. Particularlyattractive, are members of a class of compounds known as oxabicyclics.Among the readily available examples of these, are6-oxabicyclo[3.1.0]hexane or cyclopentene oxide (bp=102° C. at 760 mmHg); 7-oxabicyclo[4.1.0]heptane or cyclohexene oxide (bp=129° C. at 760mm Hg); 9-oxabicyclo[6.1.0]nonane or cyclooctene oxide (bp=55° C. at 5mm Hg); and 7-oxabicyclo[2.2.1]heptane or 1,4-epoxycyclohexane (bp=119°C. at 713 mm Hg). More generally, species that fit the formula shown inFIG. 1 may be considered suitable.

[0039] Additionally, the second precursor may have some degree ofunsaturation as in 9-oxabicylo[6.1.0]non-4-ene (bp=195° C. at 760 mm Hg)or compounds of the general structure shown in FIG. 2. Furthermore, thesecond precursor may have additional functionalities including, but notlimited to: ketones, aldehydes, amines, amides, imides, ethers, esters,anhydrides, carbonates, thiols, thioethers and the like, as in7-oxabicyclo[4.1.0]heptan-2-one (bp=77° C. at 15 mmHg) and3-oxabicyclo[3.1.0]hexane-2,4-dione (bp=100° C. at 5 mmHg).

[0040] Furthermore, the first precursor is further mixed with an inertas a carrier gas or the first and second precursor gases are mixed withan inert in the PECVD reactor. The addition of inert gas to the firstprecursor as a carrier gas, or the addition of inert gas to the firstand second precursors in the PECVD reactor provides a stabilizing effecton plasma in the PECVD reactor and improves the uniformity of the filmdeposited on the substrate.

[0041] When He is admixed with the first and second precursors, theamount of He may be from about 25 sccm to about 10,000 sccm, and morepreferably from about 50 sccm to about 5000 sccm. More preferably, theamount of He is from about 50 sccm to about 5000 sccm.

[0042] As shown in FIG. 3, parallel plate plasma enhanced chemical vapordeposition (“PECVD) reactor 10 is the type used for processing 200 mmwafers. The inner diameter, X, of the reactor 10 is approximately 13inches, while its height, Y, is approximately 8.5 inches. The diameterof substrate chuck 12 is approximately 10.8 inches. Reactant gases areintroduced into reactor 10 through a gas distribution plate (“GDP”) 16that is spaced apart from substrate chuck 12 by a gap Z of about 1 inch,and are exhausted out of reactor 10 through a 3-inch exhaust port 18. RFpower 20 is connected to GDP 16, which is electrically insulated fromreactor 10, and substrate chuck 12 is grounded. For practical purposes,all other parts of the reactor are grounded. In a different embodiment,RF power 20 can be connected to substrate chuck 12 and transmitted tosubstrate 22. In this case, the substrate acquires a negative bias,whose value is dependent on the reactor geometry and plasma parameters.In another embodiment, more than one electrical power supply can beused. For instance, two power supplies can operate at the same RFfrequency, or one may operate at a low frequency and one at a highfrequency. The two power supplies may be connected both to the sameelectrode or to separate electrodes. In another embodiment, the RF powersupply can be pulsed on and off during deposition. Process variablescontrolled during deposition of the low-k films are RF power, precursormixture and flow rate, pressure in reactor, and substrate temperature.

[0043] Surfaces 24 of reactor 10 may be coated with an insulatingcoating material. For instance, one specific type of coating is appliedon reactor walls 24 to a thickness of several mils. Another type ofcoating material that may be used on substrate chuck 12 is a thincoating of alumina or other insulator resistant to etching with anoxygen plasma. The temperature of the heated wafer chuck controls thesubstrate temperature.

[0044] In accordance the present invention, suitable first and secondprecursors and specific combination of processing parameters describedherein above are employed such that the inventive ultralow-k materialprepared preferably comprises: between about 5 and about 40 atomicpercent of Si; between about 5 and about 45 atomic percent of C; between0 and about 50 atomic percent of O; and between about 10 and about 55atomic percent of H. The main process variables controlled during adeposition process for a film are the RF power, the flow rates of theprecursors, the reactor pressure and the substrate temperature. Providedherein below are several examples of deposition of films from a firstprecursor tetramethylcyclotetrasiloxane (TMCTS) and a second precursorcyclopentene oxide (“CPO”) according to the present invention. In theexamples, the TMCTS precursor vapors were transported into the reactorby using He as a carrier gas. Optionally, the films were heat treated at400° C. after deposition to reduce k.

[0045] It should be emphasized that the fabricating method according tothe present invention is only possible by utilizing a deposition reactorthat has a specific geometry with uniquely defined growth conditions.When a reactor of different geometry is used under the defined growthconditions, the films produced may not achieve the ultralow dielectricconstant. For instance, the parallel plate reactor according to thepresent invention should have an area of the substrate chuck of betweenabout 300 cm² and about 800 cm², and preferably between about 500 cm²and about 600 cm². The gap between the substrate and the gasdistribution plate (or top electrode) is between about 1 cm and about 10cm, and preferably between about 1.5 cm and about 7 cm. A RF power isapplied to one of the electrodes at a frequency between about 12 MHZ andabout 15 MHZ, and preferably at about 13.56 MHZ. A low frequency, below1 MHz, power can optionally be applied at the same electrode as the RFpower, or to the opposite electrode at a power density of 0 to 1.5W/cm².

[0046] The deposition conditions utilized are also critical to enable asuccessful implementation of the deposition process according to thepresent invention. For instance, a wafer temperature of between about25° C. and about 325° C., and preferably of between about 60° C. andabout 200° C. is utilized. A RF power density between about 0.05 W/cm²and about 4.0 W/cm², and preferably between about 0.25 W/cm² and about 4W/cm² is utilized. In some embodiments, the RF power density is fromgreater than 1.0 W/cm² to about 4.0 W/cm². A reactant gas flow rate ofTMCTS between about 5 sccm and about 1000 sccm, and preferably betweenabout 25 sccm and about 200 sccm is utilized. A reactant gas flow rateof CPO between about 5 sccm and about 50,000 sccm, and preferablybetween about 25 sccm and about 10,000 sccm is utilized. In someembodiments, the reactant gas flow rate of CPO is greater than 1000 sccmto about 50,000 sccm.

[0047] In some embodiments of the present invention, He is added to theabove mentioned TMCTS-CPO mixture at a flow rate between about 50 sccmand 5000 sccm. A total reactant gas flow rate of TMCTS-He, where He isused as a carrier gas is from about 25 sccm to about 10,000 sccm. Atotal reactant gas flow rate of TMCTS-He, where He is used as a carriergas is preferably from about 50 sccm to 5000 sccm.

[0048] Reactor pressure during the deposition process between about 50mTorr and about 5000 mTorr, and preferably between about 100 mTorr andabout 3000 mTorr is utilized.

[0049] It should be noted that a change in the area of the substratechuck by a factor, X, i.e., a change from a value in the range betweenabout 300 cm² and about 800 cm², will change the RF power by a factor,X, from that previously specified. Similarly, a change in the area ofthe substrate chuck by a factor, Y, and a change in the gap between thegas distribution plate and the substrate chuck by a factor, Z, from thatpreviously specified, will be associated with a change by a factor, YZ,in the gas flow rates from that previously specified. If a multistationdeposition reactor is used, the area of the substrate refers to eachindividual substrate chuck and the flow rates of the gases refer to oneindividual deposition station. Accordingly, total flow rates and totalpower input to the reactor are multiplied by a total number ofdeposition stations inside the reactor.

[0050] The deposited films are stabilized before undergoing furtherintegration processing. The stabilization process can be performed in afurnace-annealing step at about 300° C. to about 450° C. for a timeperiod between about 0.5 hours and about 4 hours. The stabilizationprocess can also be performed in a rapid thermal annealing process attemperatures above about 300° C. The dielectric constants of the filmsobtained according to the present invention are lower than about 2.8.The thermal stability of the films obtained according to the presentinvention in non-oxidizing ambient is up to a temperature of about 400°C.

[0051] The electronic devices formed according to the present inventionare shown in FIGS. 6-9. It should be noted that the devices shown inFIGS. 6-9, are merely illustrated as examples according to the presentinvention, while countless other devices can also be formed according tothe present invention.

[0052]FIG. 6 depicts electronic device 30 that is built on a siliconsubstrate 32. On top of silicon substrate 32, insulating material layer34 is formed with a first region of metal 36 embedded therein. After achemical mechanical polishing (“CMP”) process is conducted on firstregion of metal 36, a film such as an ultralow-k film 38 is deposited ontop of first layer of insulating material 34 and first region of metal36. First layer of insulating material 34 may be suitably formed ofsilicon oxide, silicon nitride, doped varieties of these materials, orany other suitable insulating materials. Ultralow-k film 38 is patternedby a photolithography process and conductor layer 40 is depositedtherein. After a CMP process on first conductor layer 40 is carried out,second layer of ultralow-k film 44 is deposited by a plasma enhancedchemical vapor deposition (“PECVD”) process overlying first ultralow-kfilm 38 and first conductor layer 40. Conductor layer 40 may bedeposited of a metallic conductive material or a non-metallic conductivematerial. For instance, a metallic conductive material of aluminum orcopper, or a non-metallic material such as nitride or polysilicon may beutilized. First conductor 40 is in electrical communication with firstregion of metal 36.

[0053] A second region of conductor 50 is formed, after aphotolithographic process in second ultralow-k film layer 44 isconducted, followed by a deposition process for the second conductormaterial. Second conductor 50 may also be deposited of either a metallicmaterial or a non-metallic material, similar to that used in depositingthe first conductor layer 40. The second region of conductor 50 is inelectrical communication with the first region of conductor 40 and isembedded in the second layer of ultralow-k insulator 44. The secondlayer of ultralow-k film is in intimate contact with the first layer ofinsulating material 38. In this specific example, the first layer ofinsulating material 38, which is an ultralow-k material according to thepresent invention, serves as an intralevel dielectric material, whilethe second layer of insulating material, i.e., the ultralow-k film 44,serves as both an intralevel and an interlevel dielectric. Based on thelow dielectric constant of the ultralow-k film, superior insulatingproperty can be achieved by first insulating layer 38 and secondinsulating layer 44.

[0054]FIG. 7 depicts electronic device 60 according to the presentinvention, similar to that of electronic device 30 shown in FIG. 6, butwith additional dielectric cap layer 62 deposited between firstinsulating material layer 38 and second insulating material layer 44.Dielectric cap layer 62 can be suitably formed of a material such assilicon oxide, silicon nitride, silicon oxynitride, silicon carbide,silicon carbo-oxide (SiCO), modified ultralow-k and their hydrogenatedcompounds, as well as refractory metal silicon nitride, wherein therefractory metal is selected the group consisting of: Ta, Zr, Hf, and W.Additional dielectric cap layer 62 functions as a diffusion barrierlayer for preventing diffusion of first conductor layer 40 into secondinsulating material layer 44 or into the lower layers, especially intolayers 34 and 32.

[0055]FIG. 8 depicts another alternate embodiment of electronic device70 according to the present invention. In electronic device 70, twoadditional dielectric cap layers 72 and 74 that act as an RIE mask andCMP (chemical-mechanical polishing) polish stop layer are used. Firstdielectric cap layer 72 is deposited on top of first insulating materiallayer 38. The function of dielectric layer 72 is to provide an end pointfor the CMP process utilized in planarizing first conductor layer 40.Polish stop layer 72 can be deposited of a suitable dielectric materialsuch as silicon oxide, silicon nitride, silicon oxynitride, siliconcarbide, silicon carbo-oxide (SiCO), modified ultralow-k and theirhydrogenated compounds, as well as refractory metal silicon nitride,wherein the refractory metal is selected from the group consisting of:Ta, Zr, Hf and W. The top surface of dielectric layer 72 is at the samelevel as first conductor layer 40. A second dielectric layer 74 can beadded on top of second insulating material layer 44 for the samepurposes.

[0056]FIG. 9 depicts still another alternate embodiment of electronicdevice 80 according to the present invention. In this alternateembodiment, an additional layer of dielectric 82 is deposited and thusdivides second insulating material layer 44 into two separate layers 84and 86. Intralevel and interlevel dielectric layer 44, as depicted inFIG. 8, is therefore divided into interlayer dielectric layer 84 andintralevel dielectric layer 86 at the boundary between interconnect 92and interconnect 94, as depicted in FIG. 9. An additional diffusionbarrier layer 96 is further deposited on top of the upper dielectriclayer 74. The additional benefits provided by this alternate embodimentof the electronic structure 80 is that the dielectric layer 82 acts as aRIE etch stop providing superior interconnect depth control.

[0057] The following examples are presented to illustrate thefabrication of the ultralow-k dielectric film in accordance with thepresent invention as well as to demonstrate advantages that can beobtained therefrom:

EXAMPLE 1

[0058] In this example, according to FIG. 3, a wafer is first preparedby introducing the wafer into reactor 10 through a slit valve 14 andpre-etching the wafer by argon gas. In this wafer preparation process,the wafer temperature is set at about 180° C. and the argon flow rate isset at about 25 sccm, to achieve a pressure of about 100 mTorr. A RFpower is then turned on to about 125 W for about 60 seconds. The RFpower and the argon gas flow are then turned off.

[0059] The TMCTS precursor is carried into the reactor reactor using Heas a carrier gas; He is at a pressure of about 5 psig at the inlet tothe TMCTS container. The ultralow-k film according to the presentinvention can be deposited by first establishing gas flows of TMCTS+Heand CPO to desired flow rates and pressure, i.e., at about 20 sccm ofTMCTS+He and about 6 sccm of CPO and about 100 mTorr. A RF power is thenturned on at about 15 W for a time period of about 50 minutes. The RFpower and the gas flow are then turned off. The wafer is then removedfrom reaction reactor 10.

[0060] To reduce the dielectric constant of the deposited films and tofurther improve their thermal stability, i.e., to make them stable attemperatures greater than 300° C., the films are post annealed toevaporate the volatile contents and to dimensionally stabilize thefilms. The post annealing process can be carried out in an annealingfurnace by the following steps. The furnace is first purged for about 5minutes (with the film samples in a load station) with nitrogen at aflow rate of about 10 liters/minute. The film samples are thentransferred into the furnace reactor to start the post annealing cycleof heating the films to about 280° C. at a heating rate of about 5°C./minute, holding at about 280° C. for about 5 minutes, heating at asecond heating rate of about 5° C./minute to about 450° C., holding atabout 450° C. for about 4 hours, turning the furnace off and allowingthe film samples to cool to a temperature of below about 100° C. Asuitable first holding temperature may be between about 280° C. andabout 300° C., while a suitable second holding temperature may bebetween about 300° C. and about 450° C.

[0061] Results of the first embodiment are now discussed in reference toFIGS. 4 and 5. FIG. 4 presents a Fourier transform infrared (“FTIR”)spectrum of a typical SiCOH film. The spectrum displays a strong Si—Oabsorption band at about 1000-1100 cm⁻¹, a Si—CH₃ absorption peak atabout 1275 cm⁻¹, a Si—H absorption band at about 2150-2250 cm⁻¹ andsmall C—H absorption peaks at about 2900-3000 cm⁻¹. The relativeintensities of the CH, SiH and SiCH₃ peaks as compared to the SiO peakof the SiCOH film are presented in Table 1 herein below.

[0062]FIG. 5 presents the FTIR spectrum obtained from an ultralow-k filmprepared from a mixture of (TMCTS+He)+CPO in accordance with the presentinvention. The spectrum displays the Si—O, Si—CH₃, and C—H absorptionpeaks, as in FIG. 4. However, the Si—H peak is missing, the intensity ofthe C—H absorption band at about 2900-3000 cm⁻¹ is much stronger for theultralow-k film than for the SiCOH film shown in FIG. 4. The relativeintensities of the CH, and SiCH₃ peaks as compared to the SiO peak forthis film are also shown in Table 1. As particularly illustrated inTable 1, the integrated area of C—H peak of the ultralow-k film is 40%of the Si—CH₃ peak, while it is only 2% of the Si—CH₃ peak in the SiCOHfilm. This is a clear indication that the ultralow-k film contains asignificant amount of a secondary CH_(x) (hydrocarbon) phase in additionto the SiCOH phase. Another characteristic of the FTIR spectrum of theultralow-k film is the splitting of the Si—O peak into two peaks atabout 1139 cm⁻¹ and about 1056 cm⁻¹, as particularly illustrated in FIG.5. TABLE 1 Relative integrated intensities of FTIR absorption peakMATERIAL CH/SiO (%) SiH/SiO (%) SiCH/SiO (%) SiCOH 2 7 5 Ultralow-k 10 04

EXAMPLE 2

[0063] In this example, a wafer is prepared as described in Example 1,but the wafer temperature is set at about 300° C. The TMCTS precursor isthen carried into the reactor using He as a carrier gas; He is at apressure of about 5 psig at the inlet to the TMCTS container. Theultralow-k film according to the present invention can be deposited byfirst establishing gas flows of TMCTS+He and CPO to desired flow ratesand pressure, i.e., at about 150 sccm of TMCTS+He and about 50 sccm ofCPO and about 2000 mTorr. A RF power is then turned on at about 150 Wfor a time period of about 10 minutes. The RF power and the gas flow arethen turned off. The wafer is then removed from the reaction reactor 10and annealed as described in Example 1.

EXAMPLE 3

[0064] In this example, a reactor containing 6 deposition stations isused. The temperature of the wafer chuck is set at about 350° C. TheTMCTS precursor is carried into the reactor using a liquid deliverysystem at a flow rate of at about 5 ml/min and the CPO is flown at arate of about 2500 sccm and the pressure is stabilized at about 3000mTorr. A total RF power of about 600 W and a low frequency power ofabout 300 W are applied to the reactor. The ultralow-k film depositionis performed on the wafer at each station with the wafer moving to thenext station after a preset time interval. The wafer is removed from thereaction reactor after passing the last deposition station, and annealedas described in Example 1.

[0065] In the foregoing examples, the plasma was operated in acontinuous mode. In Example 4 herein below, the plasma is operated in apulsed mode.

EXAMPLE 4

[0066] In this example, the deposition is performed under conditionssimilar to Example 1, but the plasma is operated in a pulsed mode, i.e.,with a duty cycle of about 50% and a plasma-on time of about 50 msec toabout 100 msec. After removal of the wafer from reactor 10, the waferwith the deposited film is annealed as described in Example 1.

EXAMPLE 5

[0067] In this example, a wafer is introduced into the reactor asdescribed in Example 1, but the wafer temperature is set at about 250°C. The ultralow-k film according to the present invention can bedeposited by first establishing gas flows of TMCTS, CPO and He at flowrates of 20 sccm, 500 sccm, and 500 sccm, respectively. The pressure inthe reactor is controlled at 2000 mTorr. A RF power is then turned on atabout 200 W for a time period of about 10 minutes. The RF power and thegas flow are then turned off. The wafer is then removed from thereaction reactor 10 and annealed as described in Example 1.

[0068] As described in the foregoing examples, the films that areprepared have dielectric constants in the range of about 2.0 to about2.25.

[0069] A rapid thermal annealing (“RTA”) process may also be used tostabilize ultralow-k films. The films obtained according to the presentinvention, are characterized by dielectric constants k less than about2.8, and are thermally stable for integration in a back-end-of-the-line(“BEOL”) interconnect structure, which is normally processed attemperatures of up to about 400° C. The teachings of the presentinvention can therefore be easily adapted in producing films asintralevel and interlevel dielectrics in back-end-of-the-line processesfor logic and memory devices.

[0070] The method and electronic structures formed according to thepresent invention have therefore been thoroughly demonstrated in theabove descriptions and in the appended drawings of FIGS. 1-9. It shouldbe emphasized that the examples of the electronic structures shown inFIGS. 6-9 are merely used to illustrate the inventive method that can beapplied in the fabrication of countless electronic devices.

[0071] While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

[0072] Furthermore, while the present invention has been particularlyshown and described with respect to a preferred embodiment and severalalternate embodiments, it is to be appreciated that those skilled in theart may readily apply these teachings to other possible variations ofthe present invention without departing from the spirit and scope of thepresent invention.

[0073] The embodiments of the present invention in which exclusiveproperty or privilege is claimed are defined below in the appendedclaims:

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:
 1. A method for fabricating a thermallystable ultralow dielectric constant film comprising the steps of:providing a plasma enhanced chemical vapor deposition (PECVD) reactor;positioning a substrate in said PECVD reactor; flowing a first precursorgas comprising cyclic siloxane molecules into said PECVD reactor;flowing at least a second precursor gas comprising organic moleculeswith ring structures having C, H and O atoms into said PECVD reactor;and depositing a film comprising Si, C, O and H and a multiplicity ofnanometer-sized pores on said substrate, said depositing is performed inthe presence of an inert gas.
 2. The method according to claim 1,further comprising the step of: mixing said first precursor gas withsaid inert carrier gas.
 3. The method according to claim 1, wherein saidPECVD reactor is of a parallel plate type reactor.
 4. The methodaccording to claim 1, wherein said film is optionally heated afterdeposition at a temperature not less than about 300° C. for at leastabout 0.25 hours.
 5. The method according to claim 1, wherein said filmhas a dielectric constant of not more than about 2.8.
 6. The methodaccording to claim 1, wherein said film has a dielectric constant of notmore than about 2.3.
 7. The method according to claim 1, wherein saidfilm has a dielectric constant in a range from about 1.5 to about 2.5.8. The method according to claim 1, wherein said film comprises: betweenabout 5 and about 40 atomic percent of Si; between about 5 and about 45atomic percent of C; between 0 and about 50 atomic percent of O; andbetween about 10 and about 55 atomic percent of H.
 9. The methodaccording to claim 1, further comprising the step of: providing aparallel plate reactor having an area of a substrate chuck between about300 cm² and about 800 cm², and a gap between the substrate and a topelectrode between about 1 cm and about 10 cm.
 10. The method forfabricating a thermally stable ultralow dielectric constant filmaccording to claim 3, said method further comprising the step of:applying a RF power to an electrode of said parallel plate PECVDreactor.
 11. The method according to claim 1, further comprising a stepof: heat treating said film at a temperature not higher than about 300°C. for a first time period and heat treating said film at a temperaturenot lower than about 300° C. for a second time period, said second timeperiod being longer than said first time period.
 12. The methodaccording to claim 11, wherein said second time period is at least aboutten times that of said first time period.
 13. The method according toclaim 1, wherein said cyclic siloxane is selected from the groupconsisting of: tetramethylcyclotetrasiloxane andoctamethylcyclotetrasiloxane.
 14. The method according to claim 1,wherein said cyclic siloxane is tetramethylcyclotetrasiloxane.
 15. Themethod according to claim 1, wherein said organic molecules comprisespecies of fused rings including ring structures that impart significantring strain, wherein said ring structures that impart significant ringstrain include rings of 3, 4, 7 or more atoms.
 16. The method accordingto claim 1, wherein said organic molecules are cyclopentene oxide. 17.The method according to claim 1, wherein said step of depositing thefilm further comprises the steps of: setting a temperature for saidsubstrate at between about 25° C. and about 400° C.; and setting an RFpower density at between 0.05 W/cm² to about 4.0 W/cm².
 18. The methodaccording to claim 1, wherein said step of depositing the film furthercomprises: setting flow rates for said cyclic siloxane at between about5 sccm and about 1000 sccm and setting a flow rate for said inert gas atbetween about 25 sccm and 10,000 sccm.
 19. The method according to claim18, wherein said flow rates for said cyclic siloxane are at betweenabout 25 sccm and about 500 sccm.
 20. The method according to claim 1,wherein said step of depositing said film further comprises: settingflow rates said for said organic molecules at between about 5 sccm andabout 50,000 sccm.
 21. The method claim 20, wherein said flow rates forsaid organic molecules are at between about 25 sccm and about 10,000sccm.
 22. The method according to claim 1, wherein said step ofdepositing said film further comprises: setting a pressure for saidPECVD reactor at between about 50 mTorr and about 5000 mTorr.
 23. Themethod according to claim 22, wherein said pressure for said PECVDreactor is between about 100 mTorr and about 5000 mTorr.
 24. The methodaccording to claim 1, wherein said step of depositing said film furthercomprises: setting a flow rate ratio of organic molecules ofcyclopentene oxide to cyclic siloxane of tetramethylcyclotetrasiloxaneto between about 1 and about
 80. 25. The method for fabricating athermally stable ultralow dielectric constant film according to claim24, wherein said flow rate ratio of said cyclopentene oxide to saidtetramethylcyclotetrasiloxane is between about 10 and about
 60. 26. Themethod according to claim 1, said method further comprising: providing aparallel plate plasma enhanced chemical vapor deposition chamber. 27.The method according to claim 1, wherein plasma in said PECVD reactor isrun in a continuous mode.
 28. The method according to claim 1, whereinplasma in said PECVD reactor is run in a pulsed mode.
 29. The methodaccording to claim 9, wherein a change in the area of said substratechuck by a factor, X, changes the RF power by a factor, X.
 30. Themethod according to claim 9, wherein a change in the area of thesubstrate chuck by a factor, Y, and a change in the gap between a gasdistribution plate and the substrate chuck by a factor, Z, changes gasflow rates by a factor, YZ, such that residence time in plasma ismaintained.
 31. The method according to claim 18, wherein when saidPECVD reactor includes a plurality of depositions stations then the flowrates of said cyclic siloxane are multiplied by a total number ofdeposition stations in said PECVD reactor.
 32. A method for fabricatinga thermally stable ultralow-k film comprising the steps of: providingparallel plate type plasma enhanced chemical vapor deposition (PECVD)reactor; positioning a pre-processed wafer on a substrate chuck havingan area between about 300 cm² and about 800 cm² and maintaining a gapbetween said wafer and a top electrode between about 1 cm and about 10cm; flowing a first precursor gas comprising cyclic siloxane moleculesinto said PECVD reactor; flowing at least a second precursor gascomprising organic molecules with ring structures having C, H and Oatoms; and depositing an ultralow-k film on said wafer in the presenceof an inert gas.
 33. A method for fabricating a thermally stableultralow-k film comprising the steps of: providing a parallel plate typeplasma enhanced chemical vapor deposition (PECVD) reactor; positioning awafer on a substrate chuck having an area between about 300 cm² andabout 800 cm², and maintaining a gap between the wafer and a topelectrode between about 1 cm and about 10 cm; flowing into said reactorover said wafer kept at a temperature between about 25° C. and about400° C., a precursor gas of a cyclic siloxane at a flow rate betweenabout 5 sccm and about 1000 sccm, and a second precursor gas of organicmolecules at a flow rate between about 5 sccm and about 50,000 sccm,while keeping a pressure in said reactor between about 50 mTorr andabout 5000 mTorr; depositing an ultralow-k film on said wafer under a RFpower density between about 0.05 W/cm² and about 4.0 W/cm²; andannealing said ultralow-k film at a temperature not less than about 300°C. for at least about 0.25 hour.
 34. A method for fabricating athermally stable ultralow-k film comprising the steps of: providing aparallel plate type plasma enhanced chemical vapor deposition (PECVD)reactor; positioning a wafer on a substrate chuck having an area betweenabout 500 cm² and about 600 cm², and maintaining a gap between the waferand a top electrode between about 1 cm and about 7 cm; flowing aprecursor gas of a cyclic siloxane into said reactor over said waferkept at a temperature between about 60° C. and about 200° C. at a flowrate between about 25 sccm and about 200 sccm and a second precursor oforganic molecules at a flow rate between about 25 sccm and about 10,000sccm while keeping a pressure in said reactor between about 100 mTorrand about 3000 mTorr; depositing an ultralow-k film on said wafer undera RF power density between about 0.25 W/cm² and about 4 W/cm²; andannealing said ultralow-k film at a temperature not less than about 300°C. for at least about 0.25 hour.